x/blog: improve modules tutorial with information on using the module

[AndreKR]

There is a new modules tutorial on blog.golang.org.

It shows how to create a module, add subdependencies, update subdependencies, etc. Unfortunately one important point is missing: How do I use the newly created module?

I think this is especially important because at this point that is kind of the only thing about modules that is unclear to me. How do I point from one module to another? With replace? Where do I put this replace? It's local to my machine after all, so it doesn't belong in the repository.

[agnivade]

@andybons @dmitshur

[andybons]

@tbpg

[tbpg]

Thank you for the feedback! I think a good next post would be something like "Writing Go Modules" but we don't have a timeline for when that would be. The replace functionality is definitely worth some attention, so if it doesn't make sense as part of that post, we should include it in another.